Carrier for electrostatic charge image development, electrostatic charge image developer, process cartridge, image forming method, and image forming apparatus

Abstract

To provide a carrier for electrostatic charge image development that is excellent in line density and void prevention properties in an obtained image.SOLUTION: A carrier for electrostatic charge image development has magnetic particles and a resin coating layer on the surface of each of the magnetic particles, and includes inorganic particles in the surface or the resin coating layer. The inorganic particles include Ti, and any one of Ca, Sr, and Ba. The average circularity of primary particles of the inorganic particles is 0.82 or more and 0.94 or less. The BET specific surface area of the magnetic particles is 0.12 m2 / g or more and 0.24 m2 / g or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electrostatic image developing carrier, an electrostatic image developer, a process cartridge, an image forming method, and an image forming apparatus. [Background technology]

[0002] Resin-coated carriers having a resin coating layer on the surface of magnetic particles are known as carriers for developing electrostatic images. The following, for example, have been disclosed as resin-coated carriers or developers containing resin-coated carriers.

[0003] Patent Document 1 describes a toner and a carrier, the toner including inorganic particles having Si-containing particles on their surfaces, the Si-containing particles having a number-average equivalent circle diameter of 5 nm to 15 nm, the carrier including core particles whose surfaces are coated with a resin-containing coating layer, the volume-average particle diameter of which is 45 μm to 70 μm, and the bulk density of which is 2.10 g / cm. 3 More than 2.50g / cm 3 The following developers are disclosed:

[0004] Patent Document 2 discloses a magnetic carrier having magnetic carrier particles each having a magnetic carrier core particle and a resin coating layer formed on the surface of the magnetic carrier core particle, and inorganic fine particles A present on the surface of the magnetic carrier particle, wherein the inorganic fine particles A have a rectangular parallelepiped particle shape, the number average particle diameter (D1) of the inorganic fine particles A is 10 nm to 60 nm, the inorganic fine particles A are surface-treated with a surface treatment agent, and the solubility parameter (SP1) (J / mol) of the resin coating layer is 1 / 2 and the solubility parameter (SP2) of the surface treatment agent (J / mol) 1 / 2 satisfies formula (1), and the coverage of the surface of the magnetic carrier with the inorganic fine particles A is 5.0 atom % to 20.0 atom % as measured by X-ray photoelectron spectroscopy (ESCA). SP1-SP2≦14.00 (1) [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-71669 [Patent Document 2] Japanese Patent Publication No. 2020-91471 Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to provide a magnetic particle having a BET specific surface area of 0.12 m or less, wherein the inorganic particles are titania, the primary particles of the inorganic particles have an average circularity of less than 0.82 or more than 0.94, or 2 / g or less than 0.24m 2 The object of the present invention is to provide a carrier for developing electrostatic images which is superior in line density and suppression of white voids in the resulting image compared to when the carrier is more than 1 / g. [Means for solving the problem]

[0007] Means for solving the above problems include the following aspects. <1> A magnetic particle and a resin coating layer on the surface of the magnetic particle, the magnetic particle having inorganic particles on the surface or contained in the resin coating layer, the inorganic particles containing Ti and any one of Ca, Sr and Ba, the average circularity of the primary particles of the inorganic particles being 0.82 to 0.94, and the BET specific surface area of the magnetic particle being 0.12 m 2 / g or more 0.24m 2 / g or less of a carrier for developing electrostatic images. <2> The circularity of the inorganic particles, which accounts for 84% of the cumulative total, exceeds 0.92. <1> 10. The carrier for developing electrostatic images according to claim 19. <3> In the inorganic particles, the ratio Mx / Mt of the molar amount Mt of Ti to the total molar amount Mx of Ca, Sr, and Ba is 0.65 or more and 0.90 or less. <1> or <2> 10. The carrier for developing electrostatic images according to claim 19. <4> The flow rate is between 26 and 34. <1> ~ <3> 10. The electrostatic image developing carrier according to claim 9, wherein the carrier is a fluororesin. <5> The resin coating layer contains an acrylic resin having an aliphatic cyclic structure and an amino group. <1> ~ <4> 10. The electrostatic image developing carrier according to claim 9, wherein the carrier is a fluororesin. <6> The resin coating layer contains an acrylic resin having a structural unit having an aliphatic cyclic structure and a structural unit having an amino group. <5> 10. The carrier for developing electrostatic images according to claim 19. <7> The average particle size is 30 μm or more and 38 μm or less <1> ~ <6> 10. The electrostatic image developing carrier according to claim 9, wherein the carrier is a fluororesin. <8> <1> ~ <7> 10. An electrostatic image developer comprising the electrostatic image developing carrier according to any one of 1 to 9 and a toner. <9> <8> and a developing means for developing an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image, the process cartridge being detachably mountable to an image forming apparatus. <10> The method includes at least a charging step of charging an image carrier, an exposure step of forming an electrostatic latent image on the surface of the image carrier, a developing step of developing the electrostatic latent image formed on the surface of the image carrier with an electrostatic image developer to form a toner image, a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a transfer receiving material, and a fixing step of fixing the toner image, wherein the electrostatic image developer is <8> 2. An image forming method using the electrostatic image developer according to claim 1. <11> an image carrier; a charging unit for charging the image carrier; an exposure unit for exposing the charged image carrier to light to form an electrostatic latent image on the image carrier; a developing unit for developing the electrostatic latent image with an electrostatic image developer to form a toner image; a transfer unit for transferring the toner image from the image carrier to a transfer receiving member; and a fixing unit for fixing the toner image, wherein the electrostatic image developer is <8> 2. An image forming apparatus, wherein the electrostatic image developer is the electrostatic image developer described in 1. [Effects of the Invention]

[0008] <1> According to the invention, the inorganic particles are titania, or the average circularity of the primary particles of the inorganic particles is less than 0.82 or more than 0.94, or the BET specific surface area of the magnetic particles is 0.12 m 2 / g or less than 0.24m 2 / g, the resulting image has excellent line density and white void suppression properties, and the electrostatic image developing carrier is therefore provided. <2> According to the invention, a carrier for developing electrostatic images is provided which has superior line density and white void suppression in the obtained image compared to when the circularity of the inorganic particles, which is 84% cumulative, is 0.92 or less. <3> According to the invention, there is provided a carrier for developing electrostatic images, which has superior line density and suppression of white voids in the obtained images, compared to when the ratio Mx / Mt of the molar amount Mt of Ti to the total molar amount Mx of Ca, Sr, and Ba in the inorganic particles is less than 0.65 or exceeds 0.90. <4> According to the invention relating to (1), a carrier for developing electrostatic images is provided which has a fluidity of less than 26 or more than 34, and which provides an image with a superior line density. <5> or <6> According to the invention, there is provided a carrier for developing electrostatic images, which has a superior line density in the obtained image compared to when the resin coating layer contains only an acrylic resin having an aliphatic cyclic structure and no amino group. <7> According to the invention, there is provided a carrier for developing electrostatic images which has a superior line density in the resulting image compared to carriers having an average particle size of less than 30 μm or more than 38 μm. <8> ~ <11> According to the invention, the inorganic particles in the carrier for developing electrostatic images are titania, or the average circularity of the primary particles of the inorganic particles is less than 0.82 or more than 0.94, or the BET specific surface area of the magnetic particles is 0.12 m 2 / g or less than 0.24m 2 / g, the electrostatic image developer, process cartridge, image forming method, or image forming apparatus are excellent in line density and suppression of white voids in the obtained image. [Brief explanation of the drawings]

[0009] [Figure 1] 1A and 1B are schematic diagrams of images used for evaluating line density and white spot suppression. [Figure 2] FIG. 2 is a schematic diagram showing an evaluation portion in the image shown in FIG. 1 for evaluating white spot suppression. [Figure 3] 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. [Figure 4] 1 is a schematic diagram illustrating an example of a process cartridge that is detachably mounted to an image forming apparatus according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described in detail. In this specification, when referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified. In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values before and after "to" as the minimum and maximum values, respectively. In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In this specification, "electrostatic image developing carrier" is also referred to as "carrier," "electrostatic image developing toner" is also referred to as "toner," and "electrostatic image developer" is also referred to as "developer."

[0011] (Electrostatic image developing carrier) The electrostatic image developing carrier according to this embodiment comprises magnetic particles and a resin coating layer on the surface of the magnetic particles, and inorganic particles are either present on the surface or contained in the resin coating layer, the inorganic particles containing Ti and any one of Ca, Sr, and Ba, the average circularity of primary particles of the inorganic particles being 0.82 to 0.94, and the BET specific surface area of the magnetic particles being 0.12 m 2 / g or more 0.24m 2 / g or less.

[0012] With conventional carriers, when fine-line images are continuously printed under low temperature and low humidity conditions, the line density can become thin. Furthermore, after continuous printing of fine-line images, when a combination image with a different density, such as a halftone image, is placed inside a solid image, the image at the boundary between the two images can go unprinted, resulting in blank spaces. This is because continuous printing of fine-line images increases the toner charge, making it difficult to achieve the desired density. The electrostatic image developing carrier according to the present embodiment contains at least inorganic particles as an external additive or in a resin coating layer, the inorganic particles containing Ti and any one of Ca, Sr, and Ba, the average circularity of primary particles of the inorganic particles being 0.82 to 0.94, and the BET specific surface area of the magnetic particles being 0.12 m 2 / g or more 0.24m 2 / g or less, when inorganic particles containing Ti and any one of Ca, Sr, and Ba are present, these inorganic particles have high dielectric properties and moderately low resistance, so that charge changes can be suppressed, and further, charge can be maintained due to the dielectric properties, and excessive charge increase due to the resistance can be suppressed. When the BET specific surface area of the magnetic particles is within the above range, an appropriate number of contact points are formed between the core and the inorganic particles, and an appropriate amount of charge leaks from the inorganic particles to the core, suppressing electrostatic attraction and repulsion and stabilizing the amount present on the carrier surface. Furthermore, when the average circularity of the primary particles of the inorganic particles is within the above range, accumulation of the inorganic particles on the carrier surface is suppressed, and the mobility on the carrier surface is also appropriate. Therefore, when the BET specific surface area and circularity are within the above ranges, the effects of each other work synergistically, so that the amount of inorganic particles on the carrier is constant and fluctuations are suppressed regardless of external conditions, and detachment of inorganic particles from the carrier, which is likely to occur during continuous printing at low image density under low temperature and low humidity conditions, can be suppressed, and this is particularly effective in reducing line density and image whiteout when printing at different image densities.

[0013] The configuration of the electrostatic image developing carrier according to this embodiment will be described in detail below.

[0014] <Average circularity of primary particles of inorganic particles> In the carrier for developing electrostatic images according to this embodiment, the average circularity of the primary particles of the inorganic particles is from 0.82 to 0.94, and from the viewpoints of the line density and suppression of white voids in the resulting image, it is preferably from 0.85 to 0.94, more preferably from 0.88 to 0.93, and particularly preferably from 0.91 to 0.93.

[0015] In this embodiment, the average circularity of inorganic particles is determined by performing image analysis on at least 300 inorganic particles to determine their circularity, creating a circularity distribution, and then averaging the circularities to determine the average circularity. From the created circularity distribution, the circularity corresponding to a cumulative 84% of the inorganic particles, as described below, is determined. The inorganic particles refer to particles present on the surface of a carrier after toner has been removed from an electrostatic image developer using an arbitrary mesh with an air blower. Furthermore, the inorganic particles are identified by mapping each element on the carrier using energy dispersive X-ray analysis (SEM-EDX), and titanic acid compounds, etc., are identified from the elements of each particle on the carrier.

[0016] <BET specific surface area of magnetic particles> In the carrier for developing electrostatic images according to this embodiment, the BET specific surface area of the magnetic particles is 0.12 m 2 / g or more 0.24m 2 / g or less, and from the viewpoint of the line density of the obtained image and the suppression of white spots, 2 / g or more 0.23m 2 / g or less, and 0.15m 2 / g or more 0.23m 2 / g or less is more preferable, and 0.16m 2 / g or more 0.22m 2 It is particularly preferable that the saturation coefficient is 1 / g or less.

[0017] The method for measuring the BET specific surface area of the magnetic particles in this embodiment is as follows. The toner is removed from the electrostatic image developer by air blowing using any mesh, and then the coating film is removed with a solvent to obtain magnetic particles. The obtained magnetic particles are placed in the cell of an SA3100 specific surface area measuring device (manufactured by Beckman Coulter), degassed at 60°C for 120 minutes, and then replaced with nitrogen by a mixed gas of nitrogen and helium (volume ratio 30:70), and measured using the continuous single-point method.

[0018] <Inorganic particles> The carrier for developing electrostatic images according to this embodiment has magnetic particles and a resin coating layer on the surface of the magnetic particles, and has inorganic particles on the surface or contained in the resin coating layer, and the inorganic particles contain Ti and any one of Ca, Sr, and Ba. The inorganic particles may be present on the surface of the carrier or may be contained in the resin coating layer. However, from the viewpoint of the line density of the obtained image and the suppression of white spots, it is preferable that the inorganic particles be present on the surface of the carrier. Furthermore, when inorganic particles are present on the surface of the carrier, they may be externally added to the carrier and adhered to the surface, or an amount of inorganic particles that can be liberated to the toner may be externally added and transferred to the carrier during the preparation of the electrostatic image developer.

[0019] Preferred examples of the inorganic particles include calcium titanate particles, strontium titanate particles, and barium titanate particles. Among these, strontium titanate particles are particularly preferred from the viewpoint of the line density of the resulting image and the ability to suppress white spots. In addition, the inorganic particles preferably contain Ti and Sr from the viewpoint of the line density of the resulting image and the ability to suppress white spots.

[0020] In the inorganic particles, the ratio Mx / Mt of the molar amount of Ti Mt to the total molar amount Mx of Ca, Sr, and Ba is preferably 0.60 or more and 0.95 or less, more preferably 0.65 or more and 0.90 or less, and particularly preferably 0.75 or more and 0.85 or less, from the viewpoints of the line density and white void suppression of the obtained image.

[0021] The method for measuring Mx / Mt in this embodiment is as follows. Each element on the carrier was mapped using energy dispersive X-ray analysis (SEM-EDX). Titanate compounds were identified from the elements of each particle on the carrier, and the coverage was calculated. Furthermore, net intensity was measured using SEM-EDX, and the net intensity ratio of particles in which Ti and Ca / Sr / Ba were synchronized was calculated. A calibration curve is prepared separately, converted into moles, the molar amounts (Mt and Mx) are determined, and Mx / Mt is calculated.

[0022] The average primary particle size of the inorganic particles is preferably from 10 nm to 100 nm, more preferably from 20 nm to 90 nm, even more preferably from 30 nm to 80 nm, and particularly preferably from 30 nm to 60 nm, from the viewpoint of the line density of the resulting image and the suppression of white voids.

[0023] In this embodiment, the primary particle size of inorganic particles refers to the diameter of a circle having the same area as the primary particle image (so-called circle equivalent diameter), and the average primary particle size of inorganic particles refers to the particle size that is the cumulative 50% from the smallest diameter side in the number-based distribution of primary particle sizes. The primary particle size of inorganic particles is determined by image analysis of at least 300 inorganic particles. The inorganic particles refer to particles present on the surface of a carrier after toner has been removed from an electrostatic image developer by air blowing using an arbitrary mesh. Furthermore, the inorganic fine particles are identified as titanic acid compounds by mapping each element on the carrier using energy dispersive X-ray analysis (SEM-EDX).

[0024] The average primary particle size of the inorganic particles can be controlled, for example, by adjusting various conditions when producing the inorganic particles by a wet process.

[0025] In this embodiment, the shape of the inorganic particles is not particularly limited, but from the viewpoint of suppressing the occurrence of fogging, it is preferable that the inorganic particles have a rounded shape rather than a cube or a rectangular parallelepiped.

[0026] The circularity at which the cumulative 84% of the inorganic particles is the circularity at which the cumulative 84% of the primary particles is the circularity at which the cumulative 84% of the primary particles is obtained. From the viewpoints of the narrow circularity number distribution, the tendency for uneven adhesion to the carrier to occur, and the line density and white void suppression of the obtained image, the circularity is preferably greater than 0.92, more preferably 0.93 or more, and particularly preferably 0.95 or more. For inorganic particles, the cumulative 84% circularity of primary particles is one index of a rounded shape, and a value exceeding 0.92 can be said to indicate a rounded shape.

[0027] In this embodiment, the inorganic particles are preferably doped with a metal element (hereinafter also referred to as a dopant) other than titanium, calcium, strontium, and barium. By including a dopant, the inorganic particles have a lower crystallinity of the perovskite structure and a rounded shape.

[0028] The dopant of the inorganic particles is not particularly limited as long as it is an element other than titanium, calcium, strontium, and barium. An element having an ionic radius that can enter the crystalline structure of the inorganic particles when ionized is preferred. From this perspective, the dopant of the inorganic particles is preferably an element having an ionic radius of 40 pm or more and 200 pm or less when ionized, more preferably an element having an ionic radius of 60 pm or more and 150 pm or less.

[0029] Specific examples of dopants for inorganic particles include lanthanoids, silica (silicon), aluminum, magnesium, calcium, barium, phosphorus, sulfur, calcium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, gallium, yttrium, zinc, niobium, molybdenum, ruthenium, rhodium, palladium, silver, indium, tin, antimony, barium, tantalum, tungsten, rhenium, osmium, iridium, platinum, and bismuth. Lanthanoids are preferably lanthanum or cerium. Among these, silica or lanthanum is preferred from the viewpoints of the line density of the resulting image and the ability to suppress white spots.

[0030] As the dopant for the inorganic particles, an element having an electronegativity of 2.0 or less is preferred from the viewpoint of preventing the inorganic particles from being excessively negatively charged. In this embodiment, the electronegativity is the Allred-Rochow electronegativity. Elements with an electronegativity of 2.0 or less include lanthanum (electronegativity 1.08), magnesium (1.23), aluminum (1.47), silica (1.74), calcium (1.04), vanadium (1.45), chromium (1.56), manganese (1.60), iron (1.64), cobalt (1.70), nickel (1.75), copper (1.75), zinc (1.66), gallium (1.82), yttrium (1.11), zirconium (1.22), niobium (1.23), silver (1.42), indium (1.49), tin (1.72), barium (0.97), tantalum (1.33), rhenium (1.46), and cerium (1.06).

[0031] From the viewpoint of achieving a rounded shape while maintaining a perovskite-type crystal structure, the amount of dopant in the inorganic particles is preferably in the range of 0.1 mol % to 20 mol % of the calcium, strontium, and barium, more preferably in the range of 0.1 mol % to 15 mol %, and even more preferably in the range of 0.1 mol % to 10 mol %.

[0032] In this embodiment, the inorganic particles are preferably inorganic particles having surfaces that have been hydrophobized, from the viewpoint of improving the function of the inorganic particles. It is presumed that hydrophobized inorganic particles repel each other on the resin-coated magnetic particles, making it easier to disperse them uniformly.

[0033] In this embodiment, the inorganic particles are preferably inorganic particles having surfaces that have been hydrophobized with a silicon-containing organic compound. Inorganic particles that have been hydrophobized with a silicon-containing organic compound are less likely to be liberated to non-image areas on the photoreceptor and are less likely to cause image defects than inorganic particles that have been hydrophobized with a treatment agent that has a strong positive charge, such as a fatty acid metal salt.

[0034] The inorganic particles preferably have a surface containing a silicon-containing organic compound in an amount of 1% by mass or more and 50% by mass or less (preferably 5% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 30% by mass or less, and even more preferably 10% by mass or more and 25% by mass or less) relative to the mass of the inorganic particles. In other words, the amount of hydrophobic treatment with the silicon-containing organic compound is preferably 1% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 40% by mass or less, even more preferably 5% by mass or more and 30% by mass or less, and even more preferably 10% by mass or more and 25% by mass or less, relative to the mass of the inorganic particles. When the amount of hydrophobic treatment is within the above range, the occurrence of fogging is easily suppressed. When the amount of hydrophobic treatment is 30 mass % or less, the occurrence of aggregates due to the hydrophobic treated surface is suppressed.

[0035] In this embodiment, the inorganic particles preferably have a moisture content of 1.5% by mass or more and 10% by mass or less. When the moisture content is 1.5% by mass or more and 10% by mass or less (more preferably 2% by mass or more and 5% by mass or less), the resistance of the inorganic particles is controlled within an appropriate range, and uneven distribution due to electrostatic repulsion between the inorganic particles is effectively suppressed. The moisture content of the inorganic particles can be controlled, for example, by producing the inorganic particles by a wet method and adjusting the temperature and time of the drying treatment. When the inorganic particles are subjected to a hydrophobic treatment, the moisture content of the inorganic particles can be controlled by adjusting the temperature and time of the drying treatment after the hydrophobic treatment.

[0036] The moisture content of the inorganic particles is measured as follows. After 20 mg of the sample is left to stand in a chamber at 22°C / 55% relative humidity for 17 hours to condition the humidity, it is heated from 30°C to 250°C at a temperature increase rate of 30°C / min in a nitrogen gas atmosphere using a thermobalance (Shimadzu TGA-50) in a room at 22°C / 55% relative humidity, and the loss on heating (mass lost by heating) is measured. The moisture content is calculated using the following formula based on the measured loss on heating. Moisture content (mass%) = (heat loss from 30°C to 250°C) ÷ (mass after humidity control before heating) × 100

[0037] The content of inorganic particles contained in the carrier for developing electrostatic images according to this embodiment is preferably 0.01% by mass or more and 0.8% by mass or less, more preferably 0.01% by mass or more and 0.5% by mass or less, even more preferably 0.02% by mass or more and 0.08% by mass or less, and still more preferably 0.04% by mass or more and 0.05% by mass or less, relative to the total mass of the carrier.

[0038] The inorganic particles may be inorganic particles themselves, or may be inorganic particles (sometimes referred to as mother particles) whose surfaces have been subjected to a hydrophobic treatment. The method for producing the inorganic particles (mother particles) is not particularly limited, but a wet production method is preferred from the viewpoint of controlling the particle size and shape.

[0039] The wet method for producing inorganic particles is, for example, a method of reacting a titanium oxide source with a calcium, strontium, or barium source while adding an alkaline aqueous solution to the mixture, followed by acid treatment. In this production method, the particle size of the inorganic particles is controlled by the mixing ratio of the titanium oxide source with the calcium, strontium, or barium source, the concentration of the titanium oxide source at the start of the reaction, the temperature and addition rate of the alkaline aqueous solution, etc.

[0040] The surface treatment of inorganic particles is carried out, for example, by preparing a treatment liquid by mixing a silicon-containing organic compound, which is a hydrophobic treatment agent, with a solvent, and mixing the inorganic particles with the treatment liquid under stirring, and then continuing to stir. After the surface treatment, a drying treatment is carried out to remove the solvent from the treatment liquid.

[0041] Examples of the silicon-containing organic compound used for the surface treatment of inorganic particles include alkoxysilane compounds, silazane compounds, and silicone oils.

[0042] Examples of alkoxysilane compounds used for the surface treatment of inorganic particles include tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, hexyltrimethoxysilane, n-octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, vinyltriethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, and hexyltriethoxysilane. Silanes include decyltriethoxysilane, dodecyltriethoxysilane, phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, phenyltriethoxysilane, benzyltriethoxysilane; dimethyldimethoxysilane, dimethyldiethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane; trimethylmethoxysilane, trimethylethoxysilane;

[0043] Examples of silazane compounds used for the surface treatment of inorganic particles include dimethyldisilazane, trimethyldisilazane, tetramethyldisilazane, pentamethyldisilazane, and hexamethyldisilazane.

[0044] Examples of silicone oils used for the surface treatment of inorganic particles include silicone oils such as dimethylpolysiloxane, diphenylpolysiloxane, and phenylmethylpolysiloxane; and reactive silicone oils such as amino-modified polysiloxane, epoxy-modified polysiloxane, carboxyl-modified polysiloxane, carbinol-modified polysiloxane, fluorine-modified polysiloxane, methacryl-modified polysiloxane, mercapto-modified polysiloxane, and phenol-modified polysiloxane.

[0045] As the solvent used in preparing the treatment liquid, when the silicon-containing organic compound is an alkoxysilane compound or a silazane compound, an alcohol (e.g., methanol, ethanol, propanol, butanol) is preferred, and when the silicon-containing organic compound is a silicone oil, a hydrocarbon (e.g., benzene, toluene, normal hexane, normal heptane) is preferred.

[0046] In the treatment liquid, the concentration of the silicon-containing organic compound is preferably 1% by mass to 50% by mass, more preferably 5% by mass to 40% by mass, and even more preferably 10% by mass to 30% by mass.

[0047] The amount of the silicon-containing organic compound used for the surface treatment is preferably 1 part by mass to 50 parts by mass, more preferably 5 parts by mass to 40 parts by mass, and even more preferably 5 parts by mass to 30 parts by mass, per 100 parts by mass of the inorganic particles.

[0048] <Magnetic particles> The magnetic particles are not particularly limited, and known magnetic particles used as a core material of a carrier can be used. Specific examples of the magnetic particles include particles of magnetic metals such as iron, nickel, and cobalt; particles of magnetic oxides such as ferrite and magnetite; resin-impregnated magnetic particles in which porous magnetic powder is impregnated with resin; and magnetic powder-dispersed resin particles in which magnetic powder is dispersed in resin.

[0049] In this embodiment, ferrite particles are suitable as the magnetic particles. In this embodiment, the ferrite particles preferably contain at least one selected from calcium oxide and strontium oxide. Calcium oxide and strontium oxide are easily incorporated into the surface of ferrite particles, and the presence of calcium or strontium on the surface of ferrite particles is thought to suppress charge leakage from the ferrite particles, thereby resulting in a relatively high charge on the carrier surface. This carrier prevents the toner from becoming low-charged in the developer, thereby further suppressing fogging and improving thin line reproducibility (e.g., suppressing thickening, crushing, or blurring of thin lines). This effect is particularly noticeable when forming a low-density image of the same color after repeatedly forming a high-density, monochromatic image at a higher speed.

[0050] In this embodiment, the ferrite particles contain at least one selected from calcium oxide and strontium oxide, and the total content of calcium and strontium is preferably 0.1% by mass or more and 2.0% by mass or less relative to the total mass of the ferrite particles. When the total content of calcium and strontium is 0.1% by mass or more relative to the total mass of the ferrite particles, charge leakage from the ferrite particles is efficiently suppressed. When the total content of calcium and strontium is 2.0% by mass or less relative to the total mass of the ferrite particles, the crystal structure of the ferrite particles is well-ordered, and the resistivity and magnetic susceptibility fall within appropriate ranges. As a result, fogging is further suppressed, and thin line reproducibility is improved (e.g., thickening, crushing, or blurring of thin lines is suppressed). From the above viewpoints, the total content of calcium element and strontium element is preferably 0.1 mass % or more and 2.0 mass % or less, more preferably 0.2 mass % or more and 1.5 mass % or less, and even more preferably 0.5 mass % or more and 1.2 mass % or less, based on the entire ferrite particles.

[0051] In this embodiment, the ferrite particles contain calcium oxide, and the calcium content is preferably 0.2 mass% or more and 2.0 mass% or less relative to the total mass of the ferrite particles. When the calcium content is 0.2 mass% or more relative to the total mass of the ferrite particles, charge leakage from the ferrite particles is efficiently suppressed. When the calcium content is 2.0 mass% or less relative to the total mass of the ferrite particles, the crystal structure of the ferrite particles is well-ordered, and the resistance value and magnetic susceptibility fall within appropriate ranges. As a result, fogging is further suppressed, and thin line reproducibility is improved (for example, thickening, crushing, or blurring of thin lines is suppressed). From the above viewpoints, the calcium element content is preferably 0.2 to 2.0 mass %, more preferably 0.5 to 1.5 mass %, and even more preferably 0.5 to 1.0 mass %, based on the total mass of the ferrite particles.

[0052] In this embodiment, the ferrite particles contain strontium oxide, and the strontium content is preferably 0.1% by mass or more and 1.0% by mass or less relative to the total mass of the ferrite particles. When the strontium content is 0.1% by mass or more relative to the total mass of the ferrite particles, charge leakage from the ferrite particles is efficiently suppressed. When the strontium content is 1.0% by mass or less relative to the total mass of the ferrite particles, the crystal structure of the ferrite particles is well-ordered, and the resistance and magnetic susceptibility are within appropriate ranges. As a result, fogging is further suppressed, and thin line reproducibility is improved (for example, thickening, crushing, or blurring of thin lines is suppressed). From the above viewpoints, the content of strontium element is preferably 0.1 mass % to 1.0 mass %, more preferably 0.4 mass % to 1.0 mass %, and even more preferably 0.5 mass % to 0.8 mass %, based on the total mass of the ferrite particles.

[0053] The contents of calcium and strontium contained in the ferrite particles are measured by X-ray fluorescence analysis. The X-ray fluorescence analysis of the ferrite particles is performed by the following method. Qualitative and quantitative analysis is performed using an X-ray fluorescence analyzer (Shimadzu Corporation, XRF1500) under the following conditions: X-ray output: 40 V / 70 mA, measurement area: 10 mm diameter, measurement time: 15 minutes. The elements to be analyzed are selected based on the elements detected in the qualitative analysis. The main elements selected are iron (Fe), manganese (Mn), magnesium (Mg), calcium (Ca), strontium (Sr), oxygen (O), and carbon (C). The mass percentage (%) of each element is calculated by referring to separately prepared calibration curve data.

[0054] The volume average particle size of the magnetic particles is, for example, 10 μm or more and 500 μm or less, preferably 20 μm or more and 180 μm or less, and more preferably 25 μm or more and 60 μm or less.

[0055] The magnetic force of the magnetic particles is, for example, 50 emu / g or more, preferably 60 emu / g or more, in terms of saturation magnetization in a magnetic field of 3000 oersteds. The saturation magnetization is measured using a vibrating sample magnetometer VSMP10-15 (manufactured by Toei Kogyo Co., Ltd.). The measurement sample is placed in a cell with an inner diameter of 7 mm and a height of 5 mm and set in the instrument. The measurement is performed by applying a magnetic field and sweeping up to a maximum of 3000 oersteds. The applied magnetic field is then reduced, and a hysteresis curve is created on recording paper. The saturation magnetization, remanent magnetization, and coercive force are determined from the curve data.

[0056] The volume resistivity of the magnetic particles is, for example, 10 5 Ω cm or more 10 9 Ω·cm or less, 10 7 Ω cm or more 10 9 Ω·cm or less is preferable. The volume resistivity (Ω·cm) of magnetic particles is measured as follows: 2 The object to be measured is placed flat on the surface of the circular jig on which the electrode plate is arranged, with a thickness of 1 mm to 3 mm, to form a layer. 2The layer is sandwiched between two electrode plates. To eliminate any gaps between the objects being measured, a 4 kg load is placed on the electrode plates placed on the layer, and then the layer thickness (cm) is measured. The electrodes above and below the layer are connected to an electrometer and a high-voltage power supply generator. A high voltage is applied to both electrodes so that the electric field becomes 103.8 V / cm, and the current value (A) that flows at this time is read. The measurement environment is a temperature of 20°C and a humidity of 50% RH. The formula for calculating the volume electrical resistivity (Ω·cm) of the object being measured is as shown below. R=E×20 / (I-I0) / L In the above formula, R represents the volume electrical resistance (Ω·cm) of the object to be measured, E represents the applied voltage (V), I represents the current value (A), I0 represents the current value (A) at an applied voltage of 0 V, and L represents the layer thickness (cm). The coefficient 20 is the area of the electrode plate (cm 2 )

[0057] <Resin coating layer> The carrier for developing electrostatic images according to this embodiment has a resin coating layer on the surface of the magnetic particles. Resins that can be used to form the resin coating layer include styrene-acrylic acid copolymers; polyolefin resins such as polyethylene and polypropylene; polyvinyl or polyvinylidene resins such as polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, and polyvinyl ketone; vinyl chloride-vinyl acetate copolymers; straight silicone resins or modified silicone resins consisting of organosiloxane bonds; fluororesins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and polychlorotrifluoroethylene; polyesters; polyurethanes; polycarbonates; amino resins such as urea-formaldehyde resins; and epoxy resins.

[0058] From the viewpoint of the line density of the image to be obtained, the resin coating layer preferably contains an acrylic resin having an aliphatic cyclic structure and an amino group, and more preferably contains an acrylic resin having a structural unit having an aliphatic cyclic structure and a structural unit having an amino group. As the aliphatic cyclic structure, a cycloalkyl group is preferred, and a cyclohexyl group is more preferred. Acrylic resins having an aliphatic cyclic structure exhibit small changes in charge amount with respect to changes in temperature and humidity, resulting in stable line density in the resulting image. In particular, a cyclohexyl group, which is a stable and large functional group with a six-membered ring, is preferred. Furthermore, acrylic resins having a cyclohexyl group are less likely to cause localized charge differences on the carrier surface, making it less likely for inorganic particles to be unevenly distributed, resulting in more stable line density. Specific examples of the acrylic resin having a cyclohexyl group include a homopolymer of an acrylic monomer having a cyclohexyl group, and a copolymer of an acrylic monomer having a cyclohexyl group and another monomer. Examples of acrylic monomers having a cyclohexyl group include cyclohexyl acrylate and cyclohexyl methacrylate. Furthermore, preferred examples of structural units having an aliphatic cyclic structure include structural units derived from cyclohexyl (meth)acrylate. From the viewpoint of the linear density of the image obtained, the acrylic resin having a structural unit with an alicyclic structure preferably contains 80% by mass or more of the structural unit with an alicyclic structure. As the acrylic monomer having an amino group, dialkylaminoalkyl(meth)acrylate is preferred, and dimethylaminoethyl(meth)acrylate is more preferred. From the viewpoint of the linear density of the image obtained, the acrylic resin having a structural unit having an amino group preferably contains 0.05% by mass or more and 5% by mass or less of the structural unit having an amino group, and more preferably 0.1% by mass or more and 3% by mass or less. Acrylic resins having amino groups have good chargeability under high humidity conditions and stable linear density. As an acrylic monomer having an amino group, dimethylaminoethyl (meth)acrylate is particularly preferred because it has a small difference in chargeability between low and high humidity conditions. When an acrylic resin containing a structural unit having an alicyclic structure and a structural unit having an amino group is included, the linear density tends to be more stable. This is because, by using them together, the relatively large alicyclic structure is present around the amino group, making the amino group less susceptible to moisture, allowing the charge to be maintained and making it easier for inorganic fine particles to be present on the carrier surface. At the same time, the alicyclic structure has reduced affinity with inorganic fine particles via moisture, preventing excessive adhesion of inorganic fine particles to the carrier, thereby stabilizing the linear density. Due to the size of the structure, a combination of cyclohexyl acrylate and dimethylamino(meth)acrylate is more preferred.

[0059] The resin coating layer may contain inorganic particles other than the inorganic particles containing Ti and any one of Ca, Sr, and Ba, for the purpose of controlling charging and resistance. Examples of inorganic particles include carbon black; metals such as gold, silver, and copper; metal compounds such as barium sulfate, aluminum borate, potassium titanate, titanium oxide, silica, zinc oxide, tin oxide, antimony-doped tin oxide, tin-doped indium oxide, and aluminum-doped zinc oxide; and resin particles coated with metals. Among these, silica particles are preferred as inorganic particles other than the inorganic particles containing Ti and any one of Ca, Sr, and Ba. The content of inorganic particles other than the inorganic particles containing Ti and any one of Ca, Sr, and Ba is preferably 15% by mass or more and 50% by mass or less, and more preferably 20% by mass or more and 40% by mass or less, relative to the total mass of the resin coating layer. When the resin coating layer has a thickness within the above range, migration of other toner external additives into the resin coating layer, which reduces the effect of the inorganic particles containing Ti and any one of Ca, Sr, and Ba, is suppressed. Furthermore, by using silica particles, migration of other toner external additives into the resin coating layer is further suppressed.

[0060] Methods for forming a resin coating layer on the surface of magnetic particles include, for example, a wet method and a dry method. The wet method is a method that uses a solvent to dissolve or disperse the resin that constitutes the resin coating layer. On the other hand, the dry method is a method that does not use the solvent.

[0061] Examples of wet manufacturing methods include an immersion method in which magnetic particles are immersed in a resin liquid for forming a resin coating layer to coat them; a spray method in which a resin liquid for forming a resin coating layer is sprayed onto the surface of magnetic particles; a fluidized bed method in which magnetic particles are fluidized in a fluidized bed and a resin liquid for forming a resin coating layer is sprayed onto them; and a kneader coater method in which magnetic particles and a resin liquid for forming a resin coating layer are mixed in a kneader coater and the solvent is removed. The resin liquid for forming the resin coating layer used in the wet manufacturing method is prepared by dissolving or dispersing the resin and other components in a solvent. The solvent is not particularly limited as long as it can dissolve or disperse the resin, and examples of the solvent that can be used include aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, and ethers such as tetrahydrofuran and dioxane.

[0062] An example of a dry manufacturing method is a method in which a mixture of magnetic particles and a resin for forming a resin coating layer is heated in a dry state to form a resin coating layer. Specifically, for example, the magnetic particles and the resin for forming the resin coating layer are mixed in a gas phase and heated to melt, thereby forming a resin coating layer.

[0063] The thickness of the resin coating layer is preferably 0.1 μm or more and 10 μm or less, and more preferably 0.3 μm or more and 5 μm or less.

[0064] The exposed ratio of the magnetic particles on the surface of the carrier is preferably 2% to 20%, more preferably 2% to 10%, and even more preferably 3% to 8%.

[0065] The exposed ratio of the magnetic particles on the surface of the carrier is determined by X-ray photoelectron spectroscopy (XPS) using the following method. The target carrier and magnetic particles with the resin coating layer removed from the target carrier are prepared. Methods for removing the resin coating layer from the resin-coated magnetic particles include, for example, dissolving the resin component in an organic solvent to remove the resin coating layer, or heating to about 800°C to eliminate the resin component and remove the resin coating layer. The carrier and the magnetic particles with the resin coating layer removed are each used as measurement samples, and the Fe (atomic %) is quantified using XPS. The exposed percentage (%) of the magnetic particles is calculated as (Fe in the resin-coated magnetic particles) ÷ (Fe in the magnetic particles) × 100.

[0066] The exposed ratio of the magnetic particles on the surface of the carrier can be controlled by the amount of resin used to form the resin coating layer, and the greater the amount of resin relative to the amount of magnetic particles, the smaller the exposed ratio.

[0067] <Career characteristics> The volume average particle size of the carrier is preferably 15 μm or more and 510 μm or less, more preferably 20 μm or more and 180 μm or less, and even more preferably 25 μm or more and 60 μm or less.

[0068] In this embodiment, the fluidity of the carrier for developing electrostatic images is preferably from 26 to 34, more preferably from 27 to 33, and particularly preferably from 29 to 31, from the viewpoint of line density in the resulting image. Unless otherwise specified, the unit of fluidity is seconds / 50 g. The fluidity of the carrier for developing electrostatic images in this embodiment is a value measured at 25° C. and 50% RH in accordance with JIS Z2502 (2020).

[0069] The magnetic force of the carrier is, for example, 40 emu / g or more, preferably 50 emu / g or more, in terms of saturation magnetization in a magnetic field of 1000 oersted. The saturation magnetization is measured in the same manner as for measuring the saturation magnetization of magnetic particles, except that the magnetic field is swept up to 1000 oersted.

[0070] The volume resistivity of the carrier (at 25°C) is, for example, 1 x 10 7 Ω cm or more 1×10 15Ω·cm or less, 1×10 8 Ω cm or more 1×10 14 Ω·cm or less is preferable, and 1×10 8 Ω cm or more 1×10 13 It is more preferable that the volume resistivity of the carrier is Ω·cm or less. The volume resistivity of the carrier is measured in the same manner as that of the magnetic particles.

[0071] (Electrostatic image developer) The developer according to this embodiment contains the toner and the carrier according to this embodiment.

[0072] The developer according to this embodiment is prepared by mixing the toner and the carrier according to this embodiment in an appropriate ratio. The mixing ratio (mass ratio) of the toner to the carrier is preferably toner:carrier=1:100 to 30:100, and more preferably 3:100 to 20:100.

[0073] <Toner for developing electrostatic images> The toner is not particularly limited, and known toners can be used. For example, a colored toner containing toner particles containing a binder resin and a colorant can be used, and an infrared absorbing toner using an infrared absorbing agent instead of a colorant can also be used. The toner may contain a release agent, various internal additives, external additives, etc.

[0074] -Binder resin- Examples of binder resins include homopolymers of monomers such as styrenes (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), (meth)acrylic acid esters (e.g., methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), and olefins (e.g., ethylene, propylene, butadiene, etc.), and vinyl resins made of copolymers of two or more of these monomers. Examples of the binder resin include non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, and modified rosin, mixtures of these with the vinyl resins, and graft polymers obtained by polymerizing vinyl monomers in the presence of these. These binder resins may be used alone or in combination of two or more.

[0075] The binder resin is preferably a polyester resin, and examples of the polyester resin include known polyester resins.

[0076] The glass transition temperature (Tg) of the polyester resin is preferably 50°C or higher and 80°C or lower, and more preferably 50°C or higher and 65°C or lower. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC), and more specifically, is determined from the "extrapolated glass transition onset temperature" described in the method for determining glass transition temperature in JIS K7121-1987 "Method for measuring transition temperature of plastics."

[0077] The weight average molecular weight (Mw) of the polyester resin is preferably 5,000 or more and 1,000,000 or less, and more preferably 7,000 or more and 500,000 or less. The number average molecular weight (Mn) of the polyester resin is preferably 2,000 or more and 100,000 or less. The molecular weight distribution Mw / Mn of the polyester resin is preferably 1.5 or more and 100 or less, and more preferably 2 or more and 60 or less. The weight average molecular weight and number average molecular weight are measured by gel permeation chromatography (GPC). Molecular weight measurements by GPC are performed using a Tosoh GPC HLC-8120GPC measuring device, a Tosoh TSKgel SuperHM-M (15 cm) column, and THF solvent. The weight average molecular weight and number average molecular weight are calculated from the measurement results using a molecular weight calibration curve prepared with monodisperse polystyrene standard samples.

[0078] It is also preferable to use a combination of a polyester resin and a vinyl resin as a binder resin. The combination of the two may be a hybrid resin (a so-called styrene-acrylic modified polyester resin) in which vinyl resin segments and polyester resin segments are chemically bonded together, or a mixed resin in which vinyl resin particles are mixed with polyester resin. When polyester resin and vinyl resin are used together, the line density in the image becomes more stable. This is because when the polyester component of the toner particles transferred to the paper melts to form an image during fixing, the vinyl resin, which melts slower than the polyester, prevents the thin lines from becoming thicker and stabilizes the density. Examples of vinyl resins include homopolymers of monomers such as styrenes (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), (meth)acrylic acid esters (e.g., methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, etc.), ethylenically unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), and olefins (e.g., ethylene, propylene, butadiene, etc.), and vinyl-based resins made of copolymers combining two or more of these monomers. These vinyl resins may be used alone or in combination of two or more.

[0079] As the vinyl resin, a styrene acrylic resin is preferred because of its incompatibility with the polyester resin when the toner is melted. Styrene-acrylic resin is a copolymer obtained by copolymerizing at least a styrene-based monomer (a monomer having a styrene skeleton) and a (meth)acrylic-based monomer (a monomer having a (meth)acryloyl group, preferably a monomer having a (meth)acryloyloxy group). Styrene-acrylic resin includes, for example, a copolymer of a styrene monomer and the above-mentioned (meth)acrylic acid ester monomer. The acrylic resin portion in the styrene-acrylic resin is either an acrylic monomer or a methacrylic monomer, or a partial structure obtained by polymerizing them. Furthermore, the term "(meth)acrylic" includes both "acrylic" and "methacrylic."

[0080] Specific examples of styrene-based monomers include styrene, alkyl-substituted styrenes (e.g., α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, etc.), halogen-substituted styrenes (e.g., 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, etc.), vinylnaphthalene, etc. The styrene-based monomers may be used alone or in combination of two or more. Of these, styrene is preferred as the styrene-based monomer in terms of ease of reaction, ease of reaction control, and availability.

[0081] Specific examples of the (meth)acrylic monomer include (meth)acrylic acid and (meth)acrylic acid esters. Examples of the (meth)acrylic acid esters include (meth)acrylic acid alkyl esters (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, n-lauryl (meth)acrylate, n-tetradecyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, amyl (meth)acrylate, neopentyl (meth)acrylate, and ... isopentyl (meth)acrylate, amyl (meth)acrylate, neopentyl (meth)acrylate, and (meth)acrylic acid alkyl esters (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isopentyl (meth)acrylate, amyl (meth) Examples of the (meth)acrylic acid monomer include isohexyl acrylate, isoheptyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, etc.), (meth)acrylic acid aryl esters (for example, phenyl (meth)acrylate, biphenyl (meth)acrylate, diphenylethyl (meth)acrylate, t-butylphenyl (meth)acrylate, terphenyl (meth)acrylate, etc.), dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, methoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, β-carboxyethyl (meth)acrylate, and (meth)acrylamide. The (meth)acrylic acid monomers may be used alone or in combination of two or more. Among these (meth)acrylic esters among the (meth)acrylic monomers, from the viewpoint of improving the fixability of the toner, (meth)acrylic esters having an alkyl group having 2 to 14 carbon atoms (preferably 2 to 10 carbon atoms, more preferably 3 to 8 carbon atoms) are preferred. Among these, n-butyl (meth)acrylate is preferred, and n-butyl acrylate is particularly preferred.

[0082] The copolymerization ratio of the styrene-based monomer to the (meth)acrylic monomer (based on mass, styrene-based monomer / (meth)acrylic monomer) is not particularly limited, but is preferably 98 / 2 to 60 / 40.

[0083] The glass transition temperature (Tg) of the styrene acrylic resin is preferably 40° C. or more and 75° C. or less, and more preferably 50° C. or more and 65° C. or less, from the viewpoint of improving the fixability of the toner. The glass transition temperature of a resin is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, the glass transition temperature of a resin is determined by the "extrapolated glass transition onset temperature" described in JIS K7121:1987 "Method for measuring transition temperatures of plastics."

[0084] The weight-average molecular weight and number-average molecular weight of styrene-acrylic resin are measured by gel permeation chromatography (GPC). Molecular weight measurements by GPC are performed using a Tosoh GPC HLC-8120GPC measuring device, a Tosoh TSKgel SuperHM-M (15 cm) column, and THF solvent. The weight-average molecular weight and number-average molecular weight are calculated from the measurement results using a molecular weight calibration curve created with monodisperse polystyrene standard samples.

[0085] The method for producing the styrene-acrylic resin is not particularly limited, and various polymerization methods (e.g., solution polymerization, precipitation polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc.) are applied. In addition, the polymerization reaction is carried out by a known operation (e.g., batchwise, semi-continuous, continuous, etc.).

[0086] The content of the binder resin is preferably 40% by mass to 95% by mass, more preferably 50% by mass to 90% by mass, and even more preferably 60% by mass to 85% by mass, based on the total mass of the toner particles.

[0087] -Coloring agent- Examples of colorants include carbon black, chrome yellow, Hansa Yellow, benzidine yellow, threne yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, Balkan orange, watch young red, permanent red, brilliant carmine 3B, brilliant carmine 6B, DuPont oil red, pyrazolone red, lithol red, rhodamine B lake, lake red C, pigment red, rose bengal, aniline blue, ultramarine blue, Examples of suitable pigments include ruco oil blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, and malachite green oxalate; dyes such as acridine, xanthene, azo, benzoquinone, azine, anthraquinone, thioindigo, dioxazine, thiazine, azomethine, indigo, phthalocyanine, aniline black, polymethine, triphenylmethane, diphenylmethane, and thiazole; and inorganic pigments such as titanium compounds, silica, and aluminum. The colorant may be used alone or in combination of two or more kinds.

[0088] The colorant may be surface-treated as needed, or may be used in combination with a dispersant. Furthermore, a plurality of colorants may be used in combination.

[0089] The content of the colorant is preferably from 1% by mass to 30% by mass, and more preferably from 3% by mass to 15% by mass, based on the total mass of the toner particles.

[0090] -Mold release agent- Examples of release agents include hydrocarbon waxes, natural waxes such as carnauba wax, rice wax, and candelilla wax, synthetic or mineral / petroleum waxes such as montan wax, and ester waxes such as fatty acid esters and montanic acid esters, but are not limited thereto.

[0091] The melting temperature of the release agent is preferably 50°C or higher and 110°C or lower, and more preferably 60°C or higher and 100°C or lower. The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC) by using the "melting peak temperature" described in the method for determining the melting temperature in JIS K7121-1987 "Method for measuring transition temperatures of plastics."

[0092] The content of the release agent is preferably from 1% by mass to 20% by mass, and more preferably from 5% by mass to 15% by mass, based on the total mass of the toner particles.

[0093] -Other additives- Examples of other additives include known additives such as magnetic materials, charge control agents, inorganic powders, etc. These additives are contained in the toner particles as internal additives.

[0094] -Characteristics of toner particles, etc.- The toner particles may be toner particles of a single layer structure, or may be toner particles of a so-called core-shell structure composed of a core (core particle) and a coating layer (shell layer) that coats the core. The toner particles of the core-shell structure may be composed of, for example, a core composed of a binder resin and, if necessary, other additives such as a colorant and a release agent, and a coating layer composed of a binder resin.

[0095] The volume average particle size (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, and more preferably 4 μm or more and 8 μm or less. The volume average particle size (D50v) of toner particles is measured using a Coulter Multisizer II (manufactured by Beckman Coulter) and an ISOTON-II (manufactured by Beckman Coulter). For measurement, 0.5 mg to 50 mg of the sample to be measured is added to 2 ml of a 5% by weight aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant. This is then added to 100 ml to 150 ml of electrolyte. The electrolyte containing the suspended sample is dispersed in an ultrasonic disperser for 1 minute, and the particle size distribution of particles ranging from 2 μm to 60 μm is measured using a Coulter Multisizer II with an aperture diameter of 100 μm. 50,000 particles are sampled.

[0096] -External additives- Examples of external additives include inorganic particles, such as SiO2, TiO2, Al2O3, CuO, ZnO, SnO2, CeO2, Fe2O3, MgO, BaO, CaO, K2O, Na2O, ZrO2, CaO·SiO2, and K2O·(TiO2). n , Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, MgSO4, SrTiO3, BaTiO3, CaTiO3, etc.

[0097] The surfaces of inorganic particles as external additives are preferably subjected to a hydrophobic treatment. The hydrophobic treatment is carried out, for example, by immersing the inorganic particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited, and examples thereof include silane coupling agents, silicone oils, titanate coupling agents, and aluminum coupling agents. These may be used alone or in combination of two or more. The amount of the hydrophobic treatment agent is preferably, for example, 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the inorganic particles.

[0098] Examples of external additives include resin particles (resin particles such as polystyrene, polymethyl methacrylate, and melamine resin), cleaning lubricants (for example, metal salts of higher fatty acids such as zinc stearate, particles of fluorine-based polymers, and higher alcohols).

[0099] The amount of the external additive added is preferably 0.01% by mass or more and 10% by mass or less, and more preferably 0.01% by mass or more and 6.0% by mass or less, based on the toner particles.

[0100] -Toner manufacturing method- The toner is obtained by producing toner particles and then externally adding an external additive to the toner particles. The toner particles may be produced by either a dry production method (e.g., a kneading and pulverization method) or a wet production method (e.g., an aggregation and coalescence method, a suspension polymerization method, a dissolution and suspension method). There are no particular restrictions on these production methods, and any known production method may be used. Among these, it is preferable to obtain toner particles by the aggregation and coalescence method.

[0101] <Image forming device, image forming method> An image forming apparatus and an image forming method according to this embodiment will be described. The image forming apparatus according to the present embodiment includes an image carrier, a charging unit that charges the surface of the image carrier, an electrostatic image forming unit that forms an electrostatic image on the surface of the charged image carrier, a developing unit that contains an electrostatic image developer and develops the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer, a transfer unit that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing unit that fixes the toner image transferred to the surface of the recording medium. The electrostatic image developer according to the present embodiment is used as the electrostatic image developer.

[0102] The image forming apparatus according to this embodiment carries out an image forming method (the image forming method according to this embodiment) that includes a charging step of charging the surface of an image carrier, an electrostatic image forming step of forming an electrostatic image on the surface of the charged image carrier, a developing step of developing the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer according to this embodiment, a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing step of fixing the toner image transferred to the surface of the recording medium.

[0103] The image forming apparatus according to the present embodiment may be any of known image forming apparatuses, such as a direct transfer type apparatus that directly transfers a toner image formed on the surface of an image carrier to a recording medium; an intermediate transfer type apparatus that primarily transfers a toner image formed on the surface of an image carrier to the surface of an intermediate transfer medium, and then secondarily transfers the toner image transferred to the surface of the intermediate transfer medium to the surface of a recording medium; an apparatus equipped with a cleaning means that cleans the surface of the image carrier after the transfer of the toner image but before charging; and an apparatus equipped with a discharging means that irradiates the surface of the image carrier with discharging light to discharge it after the transfer of the toner image but before charging. When the image forming apparatus according to the present embodiment is an apparatus of the intermediate transfer type, the transfer means is configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer means for primarily transferring the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer body, and a secondary transfer means for secondarily transferring the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

[0104] In the image forming apparatus according to the present embodiment, for example, the portion including the developing means may have a cartridge structure (process cartridge) that is detachably attached to the image forming apparatus. As the process cartridge, for example, a process cartridge equipped with developing means that accommodates the electrostatic image developer according to the present embodiment is suitably used.

[0105] An example of an image forming apparatus according to the present embodiment will be described below, but the present invention is not limited to this. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.

[0106] FIG. 3 is a schematic diagram showing the configuration of the image forming apparatus according to this embodiment. The image forming apparatus shown in Figure 3 includes first through fourth electrophotographic image forming units 10Y, 10M, 10C, and 10K (image forming means) that output images in the colors yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. These image forming units (hereinafter sometimes simply referred to as "units") 10Y, 10M, 10C, and 10K are arranged side by side horizontally spaced a predetermined distance apart from one another. These units 10Y, 10M, 10C, and 10K may be process cartridges that are detachably attached to the image forming apparatus.

[0107] An intermediate transfer belt (an example of an intermediate transfer body) 20 is provided above each of the units 10Y, 10M, 10C, and 10K and extends through each unit. The intermediate transfer belt 20 is provided wrapped around a drive roll 22 and a support roll 24, and runs in a direction from the first unit 10Y to the fourth unit 10K. A force is applied to the support roll 24 by a spring or the like (not shown) in a direction away from the drive roll 22, and tension is applied to the intermediate transfer belt 20 wrapped around them. An intermediate transfer body cleaning device 30 is provided on the image carrier side of the intermediate transfer belt 20, facing the drive roll 22. The developing devices (examples of developing means) 4Y, 4M, 4C, and 4K of the units 10Y, 10M, 10C, and 10K are supplied with yellow, magenta, cyan, and black toner contained in toner cartridges 8Y, 8M, 8C, and 8K, respectively.

[0108] Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration and operation, we will explain here the first unit 10Y, which forms a yellow image and is arranged upstream in the direction of travel of the intermediate transfer belt.

[0109] The first unit 10Y has a photoreceptor 1Y that acts as an image carrier. Around the photoreceptor 1Y, there are arranged in this order: a charging roll (an example of a charging means) 2Y that charges the surface of the photoreceptor 1Y to a predetermined potential; an exposure device (an example of an electrostatic image forming means) 3 that exposes the charged surface to a laser beam 3Y based on a color-separated image signal to form an electrostatic image; a developing device (an example of a developing means) 4Y that supplies charged toner to the electrostatic image to develop it; a primary transfer roll 5Y (an example of a primary transfer means) that transfers the developed toner image onto an intermediate transfer belt 20; and a photoreceptor cleaning device (an example of a cleaning means) 6Y that removes toner remaining on the surface of the photoreceptor 1Y after the primary transfer. The primary transfer roll 5Y is disposed inside the intermediate transfer belt 20 and is provided at a position facing the photoreceptor 1Y. A bias power supply (not shown) that applies a primary transfer bias is connected to the primary transfer rolls 5Y, 5M, 5C, and 5K of each unit. Each bias power supply changes the value of the transfer bias applied to each primary transfer roll under the control of a control unit (not shown).

[0110] The operation of forming a yellow image in the first unit 10Y will be described below. First, prior to operation, the surface of the photosensitive member 1Y is charged to a potential of −600V to −800V by the charging roll 2Y. The photoconductor 1Y has conductivity (for example, a volume resistivity of 1×10 at 20°C). -6 The photosensitive layer is formed by laminating a photosensitive layer on a substrate with a resistivity of Ωcm or less. This photosensitive layer normally has a high resistance (the resistance of ordinary resins), but when irradiated with a laser beam, the resistivity of the irradiated portion changes. Therefore, the exposed surface of the photosensitive element 1Y is irradiated with a laser beam 3Y from the exposure device 3 in accordance with image data for yellow sent from a control unit (not shown). This forms an electrostatic charge image of a yellow image pattern on the surface of the photosensitive element 1Y.

[0111] An electrostatic image is an image formed on the surface of the photosensitive element 1Y by charging it; the laser beam 3Y reduces the resistivity of the irradiated portion of the photosensitive layer, causing the charged charges on the surface of the photosensitive element 1Y to flow, while the charges remain in the portions not irradiated by the laser beam 3Y, forming a so-called negative latent image. The electrostatic image formed on the photoreceptor 1Y rotates to a predetermined development position as the photoreceptor 1Y moves, and at this development position, the electrostatic image on the photoreceptor 1Y is developed into a toner image by the developing device 4Y and made visible.

[0112] The developing device 4Y contains an electrostatic image developer containing, for example, at least yellow toner and a carrier. The yellow toner is frictionally charged by being stirred inside the developing device 4Y, and is held on a developer roll (an example of a developer holder) with a charge of the same polarity (negative polarity) as the charge on the photoreceptor 1Y. As the surface of the photoreceptor 1Y passes through the developing device 4Y, the yellow toner electrostatically adheres to the discharged latent image portion on the surface of the photoreceptor 1Y, and the latent image is developed with the yellow toner. The photoreceptor 1Y on which the yellow toner image has been formed continues to travel at a predetermined speed, and the toner image developed on the photoreceptor 1Y is transported to a predetermined primary transfer position.

[0113] When the yellow toner image on the photoreceptor 1Y is transported to the primary transfer position, a primary transfer bias is applied to the primary transfer roll 5Y, and an electrostatic force from the photoreceptor 1Y to the primary transfer roll 5Y acts on the toner image, causing the toner image on the photoreceptor 1Y to be transferred onto the intermediate transfer belt 20. The transfer bias applied at this time has a (+) polarity opposite to the (-) polarity of the toner, and is controlled to, for example, +10 μA by a control unit (not shown) in the first unit 10Y. On the other hand, the toner remaining on the photoreceptor 1Y is removed and collected by the photoreceptor cleaning device 6Y.

[0114] The primary transfer bias applied to the primary transfer rolls 5M, 5C, and 5K of the second unit 10M and subsequent units is also controlled in accordance with the first unit. In this way, the intermediate transfer belt 20 onto which the yellow toner image has been transferred by the first unit 10Y is conveyed sequentially through the second to fourth units 10M, 10C, and 10K, and the toner images of each color are superimposed and transferred.

[0115] The intermediate transfer belt 20, onto which the four-color toner images have been multiplex-transferred through the first to fourth units, reaches a secondary transfer section composed of the intermediate transfer belt 20, a support roll 24 in contact with the inner surface of the intermediate transfer belt, and a secondary transfer roll (an example of a secondary transfer means) 26 arranged on the image bearing surface side of the intermediate transfer belt 20. Meanwhile, recording paper (an example of a recording medium) P is fed via a feed mechanism into the gap between the secondary transfer roll 26 and the intermediate transfer belt 20 at a predetermined timing, and a secondary transfer bias is applied to the support roll 24. The transfer bias applied at this time has a negative polarity, the same as the negative polarity of the toner. Electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, transferring the toner image on the intermediate transfer belt 20 onto the recording paper P. The secondary transfer bias at this time is determined according to resistance detected by resistance detection means (not shown) that detects resistance in the secondary transfer section, and is voltage-controlled.

[0116] Thereafter, the recording paper P is sent to the pressure contact portion (nip portion) of a pair of fixing rolls in a fixing device (an example of fixing means) 28, where the toner image is fixed onto the recording paper P, forming a fixed image.

[0117] Examples of the recording paper P onto which the toner image is transferred include plain paper used in electrophotographic copiers, printers, etc. In addition to the recording paper P, examples of the recording medium include overhead projector sheets and the like. To further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording paper P is also smooth. For example, coated paper in which the surface of plain paper is coated with resin or the like, or art paper for printing, etc., is preferably used.

[0118] The recording paper P on which the color image has been fixed is conveyed toward the discharge section, and the series of color image forming operations is completed.

[0119] <Process cartridge> The process cartridge according to this embodiment will be described. The process cartridge according to this embodiment is a process cartridge that is detachably attached to an image forming apparatus and that contains the electrostatic image developer according to this embodiment and is equipped with a developing means that develops an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image.

[0120] The process cartridge according to this embodiment is not limited to the above configuration, but may also be configured to include a developing means and, if necessary, at least one other means selected from an image carrier, a charging means, an electrostatic image forming means, and a transfer means.

[0121] An example of a process cartridge according to the present embodiment will be described below, but the present invention is not limited to this. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.

[0122] FIG. 4 is a schematic diagram showing the configuration of the process cartridge according to the present embodiment. The process cartridge 200 shown in FIG. 4 is configured to integrally combine and hold a photosensitive member 107 (an example of an image carrier), a charging roll 108 (an example of a charging means) provided around the photosensitive member 107, a developing device 111 (an example of a developing means), and a photosensitive member cleaning device 113 (an example of a cleaning means), which are combined and held together by a housing 117 having, for example, a mounting rail 116 and an opening 118 for exposure, to form a cartridge. In FIG. 4, 109 denotes an exposure device (an example of an electrostatic image forming means), 112 denotes a transfer device (an example of a transfer means), 115 denotes a fixing device (an example of a fixing means), and 300 denotes recording paper (an example of a recording medium). [Example]

[0123] Hereinafter, the present embodiment will be described in detail by way of examples. However, the present embodiment is not limited to these examples in any way. In the following description, unless otherwise specified, all "parts" and "%" are based on mass.

[0124] <Measurement of BET specific surface area of magnetic particles> Using an arbitrary mesh, toner was removed from the electrostatic charge image developer by air blowing. Then, the coating film was removed with a solvent to obtain magnetic particles. The obtained magnetic particles were placed in a cell of a SA3100 specific surface area measuring device (manufactured by Beckman Coulter), degassed at 60 °C for 120 minutes, nitrogen-substituted with a mixed gas of nitrogen and helium (volume ratio 30:70), and measured by the continuous single-point method.

[0125] <Measurement of circularity distribution and average circularity of inorganic particles> The average circularity of the inorganic particles was determined by obtaining the circularity by image analysis of at least 三百個 inorganic particles, creating a circularity distribution, and taking the average of the circularities to obtain the average circularity. Also, from the circularity distribution, the circularity corresponding to 84% cumulative of the inorganic particles was obtained. The inorganic particles are particles present on the surface of the carrier from which toner has been removed by air blowing using an arbitrary mesh from the electrostatic charge image developer, and the inorganic particles were identified and measured from the elements of each particle on the carrier by energy dispersive X-ray analysis (SEM-EDX) by mapping each element on the carrier.

[0126] <Measurement of molar amount Mt of Ti and total molar amount Mx of Ca, Sr and Ba and ratio Mx / Mt> By energy dispersive X-ray analysis (SEM-EDX), each element on the carrier was mapped. From the elements of each particle on the carrier, a titanate compound was identified and the coating rate was calculated. Further, the net intensity was measured by SEM-EDX, and the net intensity ratio of particles in which Ti and Ca / Sr / Ba are synchronized was calculated. A calibration curve was separately created, converted into moles, the molar amounts (Mt and Mx) were obtained, and Mx / Mt was calculated.

[0127] <Volume average particle diameter of carrier> It should be noted that the number "三百個" in the original text seems incorrect. It might be a typo. If it is supposed to be a specific number, please correct it for a more accurate translation.The toner was removed from the electrostatic image developer using an arbitrary mesh with an air blower, and the carrier was taken out. The particle size distribution of the carrier was measured using a laser diffraction / scattering particle size distribution analyzer (LS Particle Size Analyzer: LS13 320, manufactured by Beckman Coulter). The obtained particle size distribution was divided into particle size ranges (channels), and the volume cumulative distribution was subtracted from the small particle size side, and the particle size at 50% of the cumulative distribution was defined as the volume average particle size D50.

[0128] <Toner Production> [Preparation of Resin Particle Dispersion (1)] Ethylene glycol (Fujifilm Wako Pure Chemical Industries, Ltd.): 37 parts Neopentyl glycol (Fujifilm Wako Pure Chemical Industries, Ltd.): 65 parts 1,9-nonanediol (Fujifilm Wako Pure Chemical Industries, Ltd.): 32 parts Terephthalic acid (Fujifilm Wako Pure Chemical Industries, Ltd.): 96 parts The above materials were charged into a flask, and the temperature was raised to 200°C over 1 hour. After confirming uniform stirring within the reaction system, 1.2 parts of dibutyltin oxide was added. The temperature was raised to 240°C over 6 hours while distilling off the resulting water. Stirring was continued at 240°C for 4 hours, yielding a polyester resin (acid value 9.4 mgKOH / g, weight-average molecular weight 13,000, glass transition temperature 62°C). This polyester resin was transferred in its molten state to an emulsifier / disperser (Cavitron CD1010, Eurotech) at a rate of 100 g / min. Separately, a 0.37% concentration dilute ammonia water, prepared by diluting reagent ammonia water with ion-exchanged water, was placed in a tank and heated to 120°C in a heat exchanger. The emulsifier / disperser was operated at a rotor speed of 60 Hz and a pressure of 5 kg / cm. 2 The operation was carried out under the conditions of (a) to (c) to obtain a resin particle dispersion (1) having a volume average particle size of 160 nm and a solid content of 30%.

[0129] [Preparation of Resin Particle Dispersion (2)] Decanedioic acid (Tokyo Chemical Industry Co., Ltd.): 81 parts Hexanediol (Fujifilm Wako Pure Chemical Industries, Ltd.): 47 parts The above materials were charged into a flask, and the temperature was raised to 160°C over 1 hour. After confirming that the reaction system was uniformly stirred, 0.03 parts of dibutyltin oxide was added. The temperature was raised to 200°C over 6 hours while distilling off the produced water, and stirring was continued at 200°C for 4 hours. The reaction liquid was then cooled, solid-liquid separation was performed, and the solid was dried at 40°C under reduced pressure to obtain polyester resin (C1) (melting point 64°C, weight average molecular weight 15,000).

[0130] Polyester resin (C1): 50 parts Anionic surfactant (Neogen SC, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 2 parts Ion-exchanged water: 200 parts The above materials were heated to 120°C and thoroughly dispersed using a homogenizer (Ultra Turrax T50, IKA), and then dispersed using a pressure discharge homogenizer. When the volume average particle size reached 180 nm, the particles were collected to obtain a resin particle dispersion (2) with a solid content of 20%.

[0131] [Preparation of Colorant Particle Dispersion (1)] Cyan pigment (Pigment Blue 15:3, manufactured by Dainichi Seika Color & Chemicals Mfg. Co., Ltd.): 10 parts Anionic surfactant (Neogen SC, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 2 parts Ion-exchanged water: 80 parts The above materials were mixed and dispersed for 1 hour using a high-pressure impact disperser (Ultimizer HJP30006, Sugino Machine Co., Ltd.) to obtain a colorant particle dispersion (1) with a volume average particle size of 180 nm and a solid content of 20%.

[0132] [Preparation of Release Agent Particle Dispersion (1)] Paraffin wax (HNP-9, manufactured by Nippon Seiro Co., Ltd.): 50 parts Anionic surfactant (Neogen SC, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 2 parts Ion-exchanged water: 200 parts The above materials were heated to 120°C and thoroughly dispersed using a homogenizer (Ultra Turrax T50, manufactured by IKA), and then dispersed using a pressure discharge homogenizer. When the volume average particle size reached 200 nm, the particles were collected to obtain a release agent particle dispersion (1) with a solid content of 20%.

[0133] [Preparation of Toner (1)] ·Resin particle dispersion (1): 150 parts ·Resin particle dispersion (2): 50 parts Colorant particle dispersion (1): 25 parts Release agent particle dispersion (1): 35 parts Polyaluminum chloride: 0.4 parts Ion-exchanged water: 100 parts The above materials were placed in a round stainless steel flask and thoroughly mixed and dispersed using a homogenizer (Ultra-Turrax T50, IKA). The flask was then heated to 48°C in an oil bath while stirring. The reaction system was maintained at 48°C for 60 minutes, and 70 parts of resin particle dispersion (1) was slowly added. The pH was then adjusted to 8.0 using a 0.5 mol / L aqueous sodium hydroxide solution. The flask was then sealed, the stirring shaft was magnetically sealed, and the mixture was heated to 90°C with continued stirring and maintained for 30 minutes. The mixture was then cooled at a rate of 5°C / min, solid-liquid separated, and thoroughly washed with ion-exchanged water. The solid-liquid separated product was then redispersed in ion-exchanged water at 30°C and washed with stirring at 300 rpm (revolutions per minute) for 15 minutes. This washing operation was repeated six more times, and when the pH of the filtrate reached 7.54 and the electrical conductivity reached 6.5 μS / cm, solid-liquid separation was performed, followed by vacuum drying for 24 hours to obtain toner particles with a volume average particle size of 5.7 μm.

[0134] 100 parts of the above toner particles and 2.5 parts of silica particles (surface hydrophobized with hexamethyldisilazane, average primary particle size 40 nm) were mixed in a Henschel mixer to obtain toner (1).

[0135] [Preparation of Resin Particle Dispersion (3)] 1,10-Decanedicarboxylic acid (Fujifilm Wako Pure Chemical Industries, Ltd.): 260 parts 1,6-Hexanediol (Fujifilm Wako Pure Chemical Industries, Ltd.): 167 parts Dibutyltin oxide (catalyst): 0.3 parts The above materials were placed in a flask, the air in the flask was replaced with nitrogen gas to create an inert atmosphere, and the mixture was stirred and refluxed at 180°C for 5 hours using mechanical stirring. The temperature was then gradually increased to 230°C under reduced pressure, and the mixture was stirred for 2 hours. When the mixture reached a viscous state, it was air-cooled to terminate the reaction. This resulted in a crystalline polyester with a weight-average molecular weight of 12,500 and a melting temperature of 73°C. 90 parts of crystalline polyester resin, 1.8 parts of anionic surfactant (TaycaPower, manufactured by Tayca Corporation, 12% solids, sodium dodecylbenzenesulfonate), and 210 parts of ion-exchanged water were mixed, heated to 120°C, and dispersed using a homogenizer (Ultra-Turrax T50 manufactured by IKA Corporation). The mixture was then dispersed for 1 hour using a pressure-discharge Gaulin homogenizer to obtain resin particle dispersion (3) with a volume average particle size of 195 nm and a solids content of 30%.

[0136] [Synthesis of amorphous polyester resin (A)] Terephthalic acid: 68 parts Fumaric acid: 32 parts Ethylene glycol: 42 parts 1,5-pentanediol: 47 parts The above materials were placed in a flask equipped with a stirrer, nitrogen inlet tube, temperature sensor, and distillation column, and the temperature was raised to 220°C over 1 hour under a nitrogen gas stream. One part of titanium tetraethoxide was then added for every 100 parts of the above materials. The temperature was raised to 240°C over 0.5 hours while distilling off the resulting water. The dehydration condensation reaction was continued at 240°C for 1 hour, after which the reaction mixture was cooled. Thus, an amorphous polyester resin (A) with a weight-average molecular weight of 97,000 and a glass transition temperature of 60°C was obtained.

[0137] [Preparation of amorphous polyester resin particle dispersion (A1)] A vessel equipped with a temperature control device and a nitrogen purge device was charged with 40 parts of ethyl acetate and 25 parts of 2-butanol to prepare a mixed solvent, and then 100 parts of amorphous polyester resin (A) was gradually added and dissolved. A 10% aqueous ammonia solution (equivalent to three times the molar amount of the acid value of the resin) was then added and stirred for 30 minutes. The atmosphere inside the vessel was then purged with dry nitrogen, the temperature was maintained at 40°C, and 400 parts of ion-exchanged water was added dropwise to the stirred mixture to emulsify it. After the addition was completed, the emulsion was returned to 25°C, yielding a resin particle dispersion containing dispersed resin particles with a volume average particle size of 195 nm. Ion-exchanged water was added to this resin particle dispersion to adjust the solids content to 20%, yielding amorphous polyester resin particle dispersion (4).

[0138] [Preparation of styrene acrylic resin particle dispersion (S1)] Styrene: 375 parts n-Butyl acrylate: 25 parts Acrylic acid: 2 parts Dodecanethiol: 24 parts Carbon tetrabromide: 4 parts The mixture obtained by mixing and dissolving the above materials was dispersed and emulsified in a flask with a surfactant solution prepared by dissolving 6 parts of a nonionic surfactant (Nonipol 400, manufactured by Sanyo Chemical Industries, Ltd.) and 10 parts of an anionic surfactant (TaycaPower, manufactured by Tayca Corporation, 12% solids, sodium dodecylbenzenesulfonate) in 550 parts of ion-exchanged water. Next, an aqueous solution prepared by dissolving 4 parts of ammonium persulfate in 50 parts of ion-exchanged water was added to the flask over a period of 20 minutes while stirring. After nitrogen substitution, the contents of the flask were heated in an oil bath with stirring until the temperature reached 70°C, and the temperature was maintained at 70°C for 5 hours to continue emulsion polymerization. This resulted in a resin particle dispersion containing dispersed resin particles with a volume average particle size of 150 nm. Ion-exchanged water was added to this resin particle dispersion to adjust the solids content to 20%, yielding a styrene-acrylic resin particle dispersion (S1).

[0139] <Production of color toner> [Preparation of cyan toner (CT1)] -First agglomerated particle formation process- Ion-exchanged water: 200 parts Colorant dispersion (Cy1): 15 parts Release agent particle dispersion (W1): 10 parts Styrene acrylic resin particle dispersion (S1): 60 parts Crystalline polyester resin particle dispersion (B1): 10 parts Amorphous polyester resin particle dispersion (A1): 310 parts The above materials were placed in a round stainless steel flask, and 0.1 N (0.1 mol / L) nitric acid was added to adjust the pH to 3.5. An aqueous magnesium chloride solution prepared by dissolving 6 parts of magnesium chloride in 30 parts of ion-exchanged water was then added. The mixture was dispersed at 30°C using a homogenizer (IKA Ultra Turrax T50), and then heated to 45°C in a heating oil bath and maintained at this temperature until the volume average particle size reached 4.5 μm.

[0140] -Second agglomerated particle formation process- Next, 5 parts of styrene-acrylic resin microparticle dispersion (S1) was added dropwise and the mixture was maintained for 30 minutes. Five parts of styrene-acrylic resin microparticle dispersion (S1) were added every 30 minutes for a total of four times. Thereafter, while continuing to stir, the pH was adjusted to 9.0 using 1N (=0.1 mol / L) aqueous sodium hydroxide solution.

[0141] -Fusion / unification process- Next, while continuing stirring, the mixture was heated to 85°C at a rate of 0.5°C / min, held at 85°C for 3 hours, and then cooled to 30°C at a rate of 15°C / min (first cooling). Next, the mixture was heated again to 85°C at a rate of 0.2°C / min, held for 30 minutes, and then cooled to 30°C at a rate of 0.5°C / min (second cooling). Next, the solid content was filtered, washed with ion-exchanged water, and dried to obtain cyan toner particles having a volume average particle size of 4.7 μm.

[0142] 100 parts of the above toner particles and 3 parts of silica particles (surface hydrophobized with hexamethyldisilazane, average primary particle size 40 nm) were mixed in a Henschel mixer to obtain toner (2).

[0143] <Magnetic particle production> [Preparation of magnetic particles 1] 1,307 parts of Fe2O3, 712 parts of Mn(OH)2, 10.5 parts of Mg(OH)2, and 20 parts of CaCO3 were mixed, and polycarboxylate, water, and 1 mm diameter zirconia beads were added as a dispersant and crushed and mixed using a sand mill. The zirconia beads were filtered off, and the filtrate was dried and then pre-fired in a rotary kiln at a rotation speed of 20 rpm and a temperature of 900°C for 2 hours. Polycarboxylate and water were added as a dispersant to the resulting pre-fired product, and 8 parts of polyvinyl alcohol were then added. The mixture was then crushed and mixed using a wet ball mill for 5 hours. The volume average particle size of the resulting crushed product was 1.2 μm. The resulting granulated product was then granulated using a spray dryer to a particle size of 34 μm. The resulting granulated product was then fired in an electric furnace at 1,420°C for 6 hours in an oxygen-nitrogen mixed atmosphere with an oxygen concentration of 1% by volume. The resulting fired product was then crushed and classified. The obtained particles were crushed and classified, then heated in a rotary kiln at 15 rpm and 900°C for 2 hours (post-processing), and further classified to obtain magnetic particles 1. The volume average particle size of magnetic particles 1 was 32 μm, and the BET specific surface area was 0.18 m. 2 / g.

[0144] [Preparation of magnetic particles 2 to 10] Magnetic particles 2 to 10 were each produced in the same manner as magnetic particle 1, except that the raw materials and various conditions were changed as shown in Table 1.

[0145] [Table 1]

[0146] <Preparation of inorganic particles> [Preparation of inorganic particles 1] 0.7 moles of desulfurized and peptized metatitanic acid, the titanium source, was collected and placed in a reaction vessel. Next, 0.77 moles of strontium chloride aqueous solution was added to the reaction vessel so that the SrO / TiO molar ratio was 1.1. Next, a solution of silicon dioxide dissolved in nitric acid was added to the reaction vessel in an amount that resulted in 2.5 moles of silicon per 100 moles of strontium. The initial TiO concentration in the mixture of the three materials was adjusted to 0.75 moles / L. The mixture was then stirred and heated to 90°C. While maintaining the temperature at 90°C and stirring, 153 mL of 10 N (=10 mol / L) aqueous sodium hydroxide solution was added over 4 hours. Stirring was then continued for another hour while maintaining the temperature at 90°C. The reaction solution was then cooled to 40°C, and hydrochloric acid was added until the pH reached 5.5, followed by stirring for 1 hour. The precipitate was then washed by repeated decantation and redispersion in water. Hydrochloric acid was added to the slurry containing the washed precipitate to adjust the pH to 6.5, and the solids were filtered off and dried. An ethanol solution of i-butyltrimethoxysilane (i-BTMS) was added to the dried solids in an amount of 20 parts i-BTMS per 100 parts solids, and the mixture was stirred for 1 hour. The solids were filtered off and dried in air at 130°C for 7 hours to obtain inorganic particles 1.

[0147] The degree of circularity can be adjusted by the temperature of the mixed solution and the amount of sodium hydroxide added. The degree of circularity can be increased by setting the temperature of the mixed solution higher, and decreased by setting the temperature of the mixed solution lower. The degree of circularity can also be adjusted by the amount of sodium hydroxide added. A small amount of sodium hydroxide increases the degree of circularity, and a large amount of sodium hydroxide decreases the degree of circularity. The degree of circularity can be adjusted by the temperature of the mixed solution and the amount of sodium hydroxide. The degree of circularity at which the cumulative 84% is reached can be adjusted by the addition time of sodium hydroxide. The longer the addition time, the greater the value of the cumulative 84% circularity, and the shorter the addition time, the smaller the value of the cumulative 84% circularity.

[0148] [Preparation of inorganic particles 2 to 17] As shown in Table 2, inorganic particles 2 to 17 were each produced in the same manner as inorganic particle 1, except that the type of dopant and the time taken for the 10N aqueous sodium hydroxide solution to be dropped were adjusted to adjust the average primary particle size, the average circularity, and the cumulative circularity to 84%. Inorganic particle 7 was produced in the same manner as inorganic particle 1, except that 12.5 moles of silicon were added per 100 moles of strontium. The dopant column for inorganic particle 7 in Table 2 states "Si poly."

[0149] [Table 2]

[0150] In Table 2 and Table 4 described later, Mx / Mt represents the ratio of the molar amount Mt of Ti to the total molar amount Mx of Ca, Sr, and Ba in the inorganic particles.

[0151] <Preparation of Coating Agent 1> Cyclohexyl methacrylate-dimethylaminoethyl methacrylate copolymer (polymerization mass ratio 99.5:0.5, weight average molecular weight 80,000): 36 parts Carbon black (VXC72, Cabot): 4 parts Melamine resin particles (Eposter S, manufactured by Nippon Shokubai Co., Ltd.): 3 parts Toluene: 180 parts Isopropanol: 30 parts The above materials and glass beads (1 mm diameter, same amount as toluene) were placed in a sand mill (Kansai Paint Co., Ltd.) and stirred at a rotation speed of 1,200 rpm for 30 minutes to prepare Coating Agent 1.

[0152] <Preparation of Coating Agent 2> Cyclohexyl methacrylate homopolymer (weight average molecular weight 80,000): 36 parts Carbon black (VXC72, Cabot): 4 parts Melamine resin particles (Eposter S, manufactured by Nippon Shokubai Co., Ltd.): 3 parts Toluene: 180 parts Isopropanol: 30 parts The above materials and glass beads (1 mm diameter, same amount as toluene) were placed in a sand mill (Kansai Paint Co., Ltd.) and stirred at a rotation speed of 1,200 rpm for 30 minutes to prepare Coating Agent 2.

[0153] <Preparation of Coating Agent 3> Cyclohexyl methacrylate-dimethylaminoethyl methacrylate copolymer (polymerization mass ratio 99.5:0.5, weight average molecular weight 80,000): 36 parts Carbon black (VXC72, Cabot): 4 parts Melamine resin particles (Eposter S, manufactured by Nippon Shokubai Co., Ltd.): 3 parts ·Inorganic particles 1:15 parts Toluene: 180 parts Isopropanol: 30 parts The above materials and glass beads (1 mm diameter, same amount as toluene) were placed in a sand mill (Kansai Paint Co., Ltd.) and stirred at a rotation speed of 1,200 rpm for 30 minutes to prepare Coating Agent 3.

[0154] <Preparation of Coating Agent 4> Coating agent 4 was prepared in the same manner as in the preparation of Coating agent 1, except that the cyclohexyl methacrylate-dimethylaminoethyl methacrylate copolymer in Coating agent 1 was changed to a methyl methacrylate polymer (weight average molecular weight 50,000).

[0155] (Examples 1 to 27 and Comparative Examples 1 to 5) <Preparation of carrier for electrostatic image development> The inorganic particles listed in Table 3 were placed in a vacuum degassing kneader in the amounts listed in Table 3, and the coating agent listed in Table 3 was also placed in the amounts listed in Table 3. The mixture was heated and depressurized while stirring, and then heated to 60°C and depressurized to atmospheric pressure -200 mmHg, stirred for 15 minutes, heated to 94°C and depressurized to atmospheric pressure -720 mmHg, and stirred for 30 minutes. The reduced pressure was then released, and the mixture was stirred and dried for 10 minutes. The resulting particles were sieved through a sieve with 75 μm openings to obtain carriers 1 to 14, respectively.

[0156] [Table 3]

[0157] 1,500 parts of the carrier shown in Table 4 below was added to a V-type mixer, and then 0.75 parts of the inorganic particles shown in Table 4 was added to the V-type mixer. The mixture was stirred for 30 minutes at 25 rpm (revolutions per minute) to obtain carriers for developing electrostatic images.

[0158] <Preparation of Electrostatic Image Developer> 120 parts of toner (1) was added to the obtained electrostatic image developing carrier in the V-type mixer and stirred at 25 rpm for 20 minutes, and then sieved through a sieve with 75 μm openings to obtain developers 1 to 30 (electrostatic image developers), respectively.

[0159] <Evaluation of line density and white spot suppression> The target electrostatic image developer was loaded into the cyan position of an ApeosPrint C5570 (manufactured by Fujifilm Business Innovation Co., Ltd.). Five 20cm long, 1.0 pt lines were printed at 2cm intervals on A4 paper. 3,000 prints were run at a speed of 55 pages per minute. The line densities of the first and 3,000th prints were compared. The C5570 parameters were adjusted to fix the toner concentration of the electrostatic image developer at 6%, and printing was performed at 12°C and 10% RH. Next, the image IM shown in Figure 1 was printed, and the print density of the area R shown in Figure 2 was confirmed. The image density of the high-density image HD was 1.8, and the image density of the low-density image LD was 0.5. (Note that each image density was measured using an X-Rite 404 densitometer.)

[0160] -Comparison of line density between L1 on the first sheet and L3 on the 3,000th sheet- G5: No difference in image density between L1 and L3 is visible even at 20x magnification G4: No visible difference, but at 20x magnification, it can be seen that the L3 line is slightly thinner. G3: No difference visually, but L3 is thinner at 20x magnification G2: Visually confirm that L3 is thin G1:L3 line is thin and thin

[0161] -Evaluation of white spot suppression (Figure 1 image comparison)- G5: No abnormalities in the area shown in Figure 2 G4: The area shown in Figure 2 is slightly thin. G3: The area shown in Figure 2 is clearly thin. G2: The area shown in Figure 2 is white. G1: The part shown in Figure 2 is missing.

[0162] The evaluation results are summarized in Table 4.

[0163] [Table 4]

[0164] The titania particles shown in Table 4 were T805 manufactured by Nippon Aerosil Co., Ltd.

[0165] As shown in Table 4, the electrostatic image developing carriers of Examples 1 to 27 were superior in line density and suppression of white spots in the resulting images compared to the electrostatic image developing carriers of Comparative Examples 1 to 5.

[0166] Example 28 Toner (2) was prepared in the same manner as toner (1), except that in toner (1), the amount of silica particles mixed in the Henschel mixer was 3.4 parts by mass, and after mixing, 1.5 parts by weight of inorganic particles 1 were added and mixed in the Henschel mixer. Next, Carrier 1 and Toner 2 were mixed in a V-type mixer under the same conditions as in the preparation of Developer 1, to obtain Developer 32. When the above-mentioned evaluations were carried out, the linear density evaluation of developer 32 was G4, and the white void suppression evaluation was G4.

[0167] (((1))) Magnetic particles and a resin coating layer on the surface of the magnetic particles, wherein inorganic particles are on the surface or contained in the resin coating layer, the inorganic particles contain Ti and any one of Ca, Sr and Ba, the average circularity of primary particles of the inorganic particles is 0.82 or more and 0.94 or less, and the BET specific surface area of the magnetic particles is 0.12 m 2 / g or more 0.24m 2 / g or less of a carrier for developing electrostatic images. (((2))) The carrier for developing electrostatic images according to (((1))), wherein the circularity of the inorganic particles, which is 84% cumulative, exceeds 0.92. (((3))) The carrier for developing electrostatic images according to (((1))) or (((2))), wherein the ratio Mx / Mt of the molar amount of Ti Mt to the total molar amount Mx of Ca, Sr, and Ba in the inorganic particles is 0.65 or more and 0.90 or less. (((4))) The carrier for developing electrostatic images according to any one of (((1))) to (((3))), which has a fluidity of 26 or more and 34 or less. (((5))) The carrier for developing electrostatic images according to any one of (((1))) to (((4))), wherein the resin coating layer contains an acrylic resin having an aliphatic cyclic structure and an amino group. (((6))) The carrier for developing electrostatic images according to (((5))), wherein the resin coating layer contains an acrylic resin having a structural unit having an aliphatic cyclic structure and a structural unit having an amino group. (((7))) The carrier for developing electrostatic images according to any one of (((1))) to (((6))), which has an average particle size of 30 μm or more and 38 μm or less. (((8))) An electrostatic image developer comprising the carrier for developing electrostatic images according to any one of ((1))) to (((7))) and a toner. (((9))) A process cartridge that is detachably attached to an image forming apparatus, which contains the electrostatic image developer described in (((8))) and is equipped with a developing means that develops an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image. (((10))) An image forming method comprising at least a charging step of charging an image carrier, an exposure step of forming an electrostatic latent image on the surface of the image carrier, a developing step of developing the electrostatic latent image formed on the surface of the image carrier with an electrostatic image developer to form a toner image, a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a transfer recipient, and a fixing step of fixing the toner image, wherein the electrostatic image developer is the electrostatic image developer described in (((8))). (((11))) An image forming apparatus comprising an image carrier, charging means for charging the image carrier, exposure means for exposing the charged image carrier to light to form an electrostatic latent image on the image carrier, developing means for developing the electrostatic latent image with an electrostatic image developer to form a toner image, transfer means for transferring the toner image from the image carrier to a transfer receiving body, and fixing means for fixing the toner image, wherein the electrostatic image developer is the electrostatic image developer described in (((8))).

[0168] According to the invention related to (((1))), the inorganic particles are titania, or the average circularity of the primary particles of the inorganic particles is less than 0.82 or more than 0.94, or the BET specific surface area of the magnetic particles is 0.12 m 2 / g or less than 0.24m 2 / g, the resulting image has excellent line density and white void suppression properties, and the electrostatic image developing carrier is therefore provided. According to the invention related to (((2))), there is provided a carrier for developing electrostatic images which is superior in line density and suppression of white voids in the obtained image compared to when the circularity of the inorganic particles, which is 84% cumulative, is 0.92 or less. According to the invention related to (((3))), there is provided a carrier for developing electrostatic images which is superior in line density and suppression of white voids in the obtained images compared to when the ratio Mx / Mt of the molar amount Mt of Ti to the total molar amount Mx of Ca, Sr, and Ba in the inorganic particles is less than 0.65 or exceeds 0.90. According to the invention related to (((4))), an electrostatic image developing carrier having a fluidity of less than 26 or more than 34 is provided, which provides an image with a superior line density compared to a carrier having a fluidity of less than 26 or more than 34. According to the inventions (((5))) or (((6))), there is provided a carrier for developing electrostatic images which has superior line density in the obtained image compared to when the resin coating layer contains only an acrylic resin which has an aliphatic cyclic structure and no amino group. According to the invention related to (((7))), a carrier for developing electrostatic images is provided which has superior line density in the obtained image compared to carriers having an average particle size of less than 30 μm or more than 38 μm. According to the inventions (((8))) to (((11))), the inorganic particles in the carrier for developing electrostatic images are titania, or the average circularity of the primary particles of the inorganic particles is less than 0.82 or more than 0.94, or the BET specific surface area of the magnetic particles is 0.12 m 2 / g or less than 0.24m 2 / g, the electrostatic image developer, process cartridge, image forming method, or image forming apparatus are excellent in line density and suppression of white voids in the obtained image. [Explanation of symbols]

[0169] IM:Image HD: High density image area LD: Low image density area R: White spot suppression evaluation area

[0170] 1Y, 1M, 1C, 1K Photoconductor (an example of an image carrier) 2Y, 2M, 2C, 2K Charging roll (an example of charging means) 3. Exposure device (an example of an electrostatic image forming means) 3Y, 3M, 3C, 3K laser beam 4Y, 4M, 4C, 4K developing device (an example of developing means) 5Y, 5M, 5C, 5K Primary transfer roll (an example of a primary transfer means) 6Y, 6M, 6C, 6K: Photoconductor cleaning device (an example of a cleaning means) 8Y, 8M, 8C, 8K toner cartridges 10Y, 10M, 10C, 10K image forming units 20 Intermediate transfer belt (an example of an intermediate transfer body) 22 Drive Roll 24 Support Roll 26 Secondary transfer roll (an example of a secondary transfer means) 28 Fixing device (an example of fixing means) 30 Intermediate transfer body cleaning device P Recording paper (an example of a recording medium)

[0171] 107 Photosensitive body (an example of an image carrier) 108 Charging roll (an example of charging means) 109 Exposure device (an example of electrostatic image forming means) 111 Developing device (an example of developing means) 112 Transfer device (an example of transfer means) 113 Photosensitive drum cleaning device (an example of cleaning means) 115 Fixing device (an example of fixing means) 116 Mounting Rail 117 Cabinet 118 Exposure opening 200 Process Cartridge 300 Recording paper (an example of a recording medium)

Claims

1. a magnetic particle and a resin coating layer on the surface of the magnetic particle; The resin coating layer has inorganic particles on its surface or contains inorganic particles therein, the inorganic particles contain Ti and any one of Ca, Sr, and Ba, the average circularity of primary particles of the inorganic particles is 0.82 or more and 0.94 or less; The BET specific surface area of the magnetic particles is 0.12 m ２ / g or more 0.24m ２ / g or less Carrier for developing electrostatic images.

2. 2. The carrier for developing electrostatic images according to claim 1, wherein the circularity of the inorganic particles, which is a cumulative 84% circularity, exceeds 0.

92.

3. 3. The carrier for developing electrostatic images according to claim 1, wherein the ratio Mx / Mt of the molar amount of Ti Mt to the total molar amount Mx of Ca, Sr and Ba in the inorganic particles is 0.65 or more and 0.90 or less.

4. 3. The carrier for developing electrostatic images according to claim 1, wherein the fluidity is 26 or more and 34 or less.

5. 3. The carrier for developing electrostatic images according to claim 1, wherein the resin coating layer contains an acrylic resin having an aliphatic cyclic structure and an amino group.

6. 6. The carrier for developing electrostatic images according to claim 5, wherein the resin coating layer contains an acrylic resin having a structural unit having an aliphatic cyclic structure and a structural unit having an amino group.

7. 3. The carrier for developing electrostatic images according to claim 1, wherein the average particle size is 30 μm or more and 38 μm or less.

8. 3. An electrostatic image developer comprising the carrier for developing electrostatic images according to claim 1 or 2 and a toner.

9. a developing unit containing the electrostatic image developer according to claim 8 and developing an electrostatic image formed on a surface of an image carrier into a toner image by using the electrostatic image developer, A process cartridge is detachably mounted in an image forming apparatus.

10. a charging step of charging at least an image carrier; an exposure step of forming an electrostatic latent image on the surface of the image carrier; a developing step of developing the electrostatic latent image formed on the surface of the image carrier with an electrostatic image developer to form a toner image; a transfer step of transferring the toner image formed on the surface of the image carrier onto a surface of a transfer receiving material; a fixing step of fixing the toner image, The electrostatic image developer is the electrostatic image developer according to claim 8. Image forming method.

11. an image carrier; a charging means for charging the image carrier; an exposure unit that exposes the charged image carrier to light to form an electrostatic latent image on the image carrier; a developing means for developing the electrostatic latent image with an electrostatic image developer to form a toner image; a transfer means for transferring the toner image from the image carrier to a transfer receiving member; a fixing means for fixing the toner image, The electrostatic image developer is the electrostatic image developer according to claim 8. Image forming device.

Images